A Randomization Permutation Test for Single Subject Mediation

Area of Science:

• Psychology
• Statistics
• Biomedical Research

Background:

• Assessing individual-level treatment effects is crucial for personalized interventions.
• Existing statistical methods often focus on group-level analyses, limiting insights into single-subject processes.
• Understanding intraindividual change mechanisms is vital for tailoring treatments.

Purpose of the Study:

• To introduce and describe a novel randomization permutation (RP) test for evaluating mediation mechanisms in a single subject.
• To extend existing permutation test methodologies to individual-level data for mediation analysis.
• To provide a statistical tool for elucidating treatment-outcome pathways within individuals.

Main Methods:

• The proposed method involves random assignment to treatment levels at each measurement occasion.
• It requires repeated measures of both the mediator and outcome variable from a single subject.
• Statistical evaluation is performed using the permutation mediation test and permutation confidence intervals for residuals.

Main Results:

• A simulation study indicated that at least eight repeated measures are necessary to adequately control Type I error rates.
• Sufficient statistical power (approaching 0.8) requires larger sample sizes, even when effect sizes are substantial.
• The RP mediation test demonstrated its potential for evaluating intraindividual treatment effects.

Conclusions:

• The randomization permutation (RP) mediation test is a valuable new method for analyzing mediation in single subjects.
• This approach can statistically evaluate how treatments influence outcomes at the individual level.
• Findings support the application of RP mediation tests in personalized medicine and tailored treatment development.